Normalize hdfs-site.xml across HA and non-HA cases (#356)
Normalize hdfs-site.xml across HA and non-HA cases (#356)

* Explicitly specify the data directory for the non-HA checkpoint
  (secondary namenode) to use (in a non-HA config)
* Rearrange some elements in the hdfs-site.xml file in a more logical order
* Use HDFS namespace (using nameservice_id) in non-HA cases as well (HA
  config already uses it). This change allows using the nameservice_id
  as a stable and simple way to reference namenodes regardless of
  whether HA is used / or not
* Configure the use of ConfiguredFailoverProxyProvider in non-HA cases
  as well (HA config already used it), so that namespace can be resolved
  to physical namenodes in all cases

[Reference from Hadoop docs](https://hadoop.apache.org/docs/current/hadoop-project-dist/hadoop-hdfs/Federation.html#Federation_Configuration) - though this is a doc for HDFS federation
the specific change in this PR is orthogonal and merely aims to
normalize hdfs-site.xml across both HA / standalone configurations.
fluo-io/fluo-deploy,fluo-io/zetten,astralway/muchos,fluo-io/fluo-deploy,astralway/muchos,fluo-io/zetten